The corpora allata (CA) of insects secrete juvenile hormone (JH) which controls morphogenesis and reproduction. Although much information is available on the physiological roles of JH, very little is known about the regulation of JH synthesis and secretion. The long-term objectives of the proposed studies are to characterize the neurohormonal factors which regulate CA activity, to elucidate their mechanisms of action and to identify the nature of the stimuli which control the activities of the CA- regulating neurosecretory centers in the brain at specific stages in development. The tobacco hornworm (Manduca sexta), which is widely used as a model for neuroendocrinological and physiological studies, will be used for the proposed studies. Research will be focused on allatinhibin (AI), a neurohormonal factor which turns off JH synthesis in the CA by inhibiting JH acid methyltransferase (JHAMT), the enzyme that catalyzes the terminal step in JH biosynthesis in lepidoptera. The specific aims of this proposal are: a) to develop and optimize an assay for AI based on its effect on JHAMT activity, b) to identify the stage in development and tissue in which AI is present in maximum amounts, c) to isolate and chemically characterize AI, d) to identify the factor(s) which control the synthesis and release of AI, and e) to purify JHAMT and to study its kinetic parameters and properties. Surgical manipulation of the neuroendocrine system, in vivo assays, in vitro analysis of JH and JH acid synthesis, techniques for enzyme purifications, enzyme inhibitors, extraction and analytical procedures for peptide hormones will be employed in these studies. These studies could have important bearing on the development of novel chemicals for the control of insects which affect the health and economy of mankind.